Power driven screw-driver



Junel9, 1934. F, RR TZ 1,963,855

POWER DRIVEN SCREW DRIVER Filed May 16, 1932 Patented June 19, 19341,963,855 POWER DRIVEN SCREW-DRIVER Frans Krata, Stuttgart, Germany,assign Robert Bosch Germany Application May 18, In Germany zclaims- Thepresent invention relates to power driven hand tools and moreparticularly to power driven screwdrivers. v In electric screwdriversthe motor when driving in screws has to overcome comparatively greatforces at the moment when the heads of bear upon the material and haveto be screwed up quite tightly. In the previous constructions,therefore, comparatively large motors were employed, which considerablyincreased the cost of the tool. Furthermore the dimensions of the toolwere so large that special handles had to be provided ror theirmanipulation.

These disadvantages are overcome, according to the invention, .by anelectric motor of small output and small diameter being employed whichcan be conveniently arranged in the handle of the tool, and forovercoming the considerable additional loads which occur when finallyscrewing up or driving home the screws, the motor is provided with aflywheel disc.

An example or construction or the invention is illustrated in theaccompanv l drawing, which shows a power screwdriver partly in elevationand artly in section.

Anelectric motorbis arrangedinacasinga, dotted lines in the drawing anddiscdsecuredonitsshaftc. This disc isconstructedsoastoactatthe same timeas aian disc this purpose has inclined, outwardly-directed openings e. a

As will be seen from the drawing, the'dimensions of the motor b, andthus of the whole casing mare kept so small, that the tool requires nospecial handle, and owing to its small weight it can be convenientlyhandled. The additional forces which arise when the screws which aretobe driventobearwiththeirheadsupon the materialandaretobefirmly acrewedmare obtainedrromtheflywheeldiscd,sov small capacity or the motorsufllces for home the screws. The ten disc cools the motor soeffectively heated even with continuous work.

Aktiengesellschai't,

' held in the hand of casing of a size adapted for cooling the motor,and for that it is not iniuriously overor to Stuttgart,

1932, Serial No. 611,738 October 19, 1931 By reason of the fact that thecombined flywheel and fan is composed mass of such weight as to kineticenergy to overcome required to finally screw up can be made of suchsmall be incapable by itself, without the assistance of I overcomingsuch additional load, and this is true, notwithstanding the fact thatthe difierence the flywheel momentum,

load and the overload is mits the use of a sma the screws, the motorsize and power as to a relatively heavy store up sui'ficient theadditional load between the normal considerable. This perlight,inexpensive motor which fits within a casing so small that it can be theoperator and the resulting assembly is not only inexpensive butexceedingly compact and light in weight and therefore easily handled andoperated.

As usual the screw driver blad to the motor axially gaging coupling forThe flywheel disc when by an engaging and diseninstance a slip-clutch.

the screw is driven in, assists the disengagement or this slip-clutch.Various changes in the form, proportion and the minor details orconstruction may be made without departing from the ficing any of theadvantage principle or sacris of the invention as defined in theappended claims.

I declare, that what I claim is:

1. In a portable power oi! an operator, an said casing, said motor andpower as to driven screwdriver, a to be held in the hand 85 electricmotor arranged in being of such small size be incapable by itself ofovercoming the overload required to finally screw up the screws afterthe scr penetrated connected ew head 911888 the material, and arelatively heavy mass to and rotating with said motor and or designedform and weight in excess or that prescribed by its mechanicalconstruction adapting said mass out in claim 1 in which the mass operateas a (an.

n screw driver as set is formed to FRANZ KRATZ.

e is connected to store sufiicient kinetic energy to overcome theadditional load required to

